Openssh

If you’re a network administrator, developer, or someone hosting a website in the cloud, you’ve probably been using tools like Putty on Windows 10 to connect to your server using Secure Shell (SSH), which works fine, but you no longer need to rely on third-party tools as the Fall Creators Update now includes a ported version of OpenSSH.

What’s Secure Shell? In case you’re unfamiliar, SSH is a networking protocol similar to Telnet and FTP that allows you to transmit data from one computer to another, but unlike other protocols, this one transmits information securely using encryption. OpenSSH is a popular app in the Linux community as it allows you to connect and manage a remote server using the SSH protocol as if you’re sitting in front of it.

Most Linux and Unix distribution create ssh keys for you during the installation of the OpenSSH server package. But it may be useful to be able re-generate new server keys from time to time. For example, when you duplicate VM (KVM or container) which contains an installed ssh package and you need to use different keys from cloned KVM VM guest. The OpenSSH Project. OpenSSH has 3 repositories available. Follow their code on GitHub.

In this guide, you’ll learn the steps to install OpenSSH on a PC running the Windows 10 Fall Creators Update using the Settings app “Optional features,” and installing the Ubuntu distro.

How to install OpenSSH using Settings

Installing the OpenSSH package directly into Windows 10 allows to use Command Prompt to connect a remote server using SSH as if it was a native component of Windows.

  1. Open Settings.

  2. Click on Apps.

  3. Click on Apps & features.

  4. Under “Apps & features,” click the Manage optional features link.

  5. Click the Add a feature button.

  6. Select the OpenSSH Client option.

  7. Click the Install button.

Once you’ve completed the steps, the Linux-based OpenSSH (beta) application will install on Windows 10.

You can always start the client by launching a Command Prompt session, and running the ssh command to use OpenSSH.

How to install OpenSSH using Ubuntu

Alternatively, you can install the Ubuntu distro for Windows 10 that already includes OpenSSH. (You’ll be using the same commands using Command Prompt on Windows 10 or using the Ubuntu console, so it doesn’t really matter which method you use.)

Install the Windows Subsystem for Linux

  1. Open Start.

  2. Search for Windows Features, in the result, and click Turn Windows features on or off.

  3. Check the Windows System for Linux option.

  4. Click OK.

  5. Click the Restart now button.

After restarting your computer, you can proceed to install Ubuntu on Windows 10.

Install Ubuntu on Windows 10

  1. Open the Microsoft Store.

  2. Search for Ubuntu.

  3. Click the Install button.

Once you’ve completed the steps, you don’t need to do anything else, because OpenSSH comes pre-installed with Ubuntu. You can launch the tool by launching Ubuntu from the Start menu, and then simply run the ssh command to use OpenSSH.

Openssh

If you have any questions about the installation of OpenSSH on Windows 10 or on how to use it, remember that you can start a conversation in the Pureinfotech forums.

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Most authentication in Windows environments is done with a username-password pair.This works well for systems that share a common domain.When working across domains, such as between on-premise and cloud-hosted systems, it becomes vulnerable to brute force intrusions.

By comparison, Linux environments commonly use public-key/private-key pairs to drive authentication which doesn't require the use of guessable passwords.OpenSSH includes tools to help support this, specifically:

  • ssh-keygen for generating secure keys
  • ssh-agent and ssh-add for securely storing private keys
  • scp and sftp to securely copy public key files during initial use of a server

This document provides an overview of how to use these tools on Windows to begin using key authentication with SSH.If you are unfamiliar with SSH key management, we strongly recommend you review NIST document IR 7966 titled 'Security of Interactive and Automated Access Management Using Secure Shell (SSH).'

About key pairs

Key pairs refer to the public and private key files that are used by certain authentication protocols.

SSH public-key authentication uses asymmetric cryptographic algorithms to generate two key files – one 'private' and the other 'public'. The private key files are the equivalent of a password, and should stay protected under all circumstances. If someone acquires your private key, they can log in as you to any SSH server you have access to. The public key is what is placed on the SSH server, and may be shared without compromising the private key.

When using key authentication with an SSH server, the SSH server and client compare the public keys for username provided against the private key. If the server-side public key cannot be validated against the client-side private key, authentication fails.

Multi-factor authentication may be implemented with key pairs by requiring that a passphrase be supplied when the key pair is generated (see key generation below).During authentication the user is prompted for the passphrase, which is used along with the presence of the private key on the SSH client to authenticate the user.

Host key generation

Public keys have specific ACL requirements that, on Windows, equate to only allowing access to administrators and System.To make this easier,

  • The OpenSSHUtils PowerShell module has been created to set the key ACLs properly, and should be installed on the server
  • On first use of sshd, the key pair for the host will be automatically generated. If ssh-agent is running, the keys will be automatically added to the local store.
Openssh server

To make key authentication easy with an SSH server, run the following commands from an elevated PowerShell prompt:

Since there is no user associated with the sshd service, the host keys are stored under ProgramDatassh.

User key generation

To use key-based authentication, you first need to generate some public/private key pairs for your client.From PowerShell or cmd, use ssh-keygen to generate some key files.

This should display something like the following (where 'username' is replaced by your user name)

You can hit Enter to accept the default, or specify a path where you'd like your keys to be generated.At this point, you'll be prompted to use a passphrase to encrypt your private key files.The passphrase works with the key file to provide 2-factor authentication.For this example, we are leaving the passphrase empty.

Openssh Linux

Now you have a public/private ED25519 key pair(the .pub files are public keys and the rest are private keys):

Openssh

Remember that private key files are the equivalent of a password should be protected the same way you protect your password.To help with that, use ssh-agent to securely store the private keys within a Windows security context, associated with your Windows login.To do that, start the ssh-agent service as Administrator and use ssh-add to store the private key.

After completing these steps, whenever a private key is needed for authentication from this client, ssh-agent will automatically retrieve the local private key and pass it to your SSH client.

Winscp

Note

It is strongly recommended that you back up your private key to a secure location,then delete it from the local system, after adding it to ssh-agent.The private key cannot be retrieved from the agent.If you lose access to the private key, you would have to create a new key pairand update the public key on all systems you interact with.

Deploying the public key

To use the user key that was created above, the public key needs to be placed on the server into a text file called authorized_keys under usersusername.ssh.The OpenSSH tools include scp, which is a secure file-transfer utility, to help with this.

To move the contents of your public key (~.sshid_ed25519.pub) into a text file called authorized_keys in ~.ssh on your server/host.

This example uses the Repair-AuthorizedKeyPermissions function in the OpenSSHUtils module which was previously installed on the host in the instructions above.

Openssh Client

These steps complete the configuration required to use key-based authentication with SSH on Windows.After this, the user can connect to the sshd host from any client that has the private key.